Evolution of the GaAs(001) surface structure during the transition from the As-rich (2x4) to the Ga-rich (4x2) reconstruction

Evolution of the GaAs(001) surface during the transition from the As-rich (2 x 4) to the Ga-rich (4 x 2) reconstruction has been studied by scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED). It has been found that the (2 x 4)-(4 x 2) transition proceeds via the formation of intermediate phases exhibiting (3 x 6) and (4 x 6) LEED patterns. STM images indicate that these phases are multi-domain. In particular, the (3 x 6) phase is locally composed of domains of the "(2 x 6)" and disordered phases, while the (4 x 6) phase in addition contains (4 x 2) domains. To explain STM images taken in a dual polarity bias mode, structural models for the "(2 x 6)" and disordered phases are proposed. These structures are electrostatically compensated via disorder of As ("2 x 6" phase) and Ga (disordered phase) dimers. A comprehensive picture of the (2 x 4)-(4 x 2) phase transition based on the analysis of the STM data is presented. (C) 1998 Elsevier Science B.V. All rights reserved.